Valuable document and method and device for examining said valuable document

ABSTRACT

The invention relates to a value document, such as a banknote ( 1 ), which includes one or more window zones ( 2 A,  2 B) with one for example optically active element each which rotates a polarization plane P 0  of polarized light L A , L B , penetrating the window zone by a defined angle. If such value documents are stacked and polarized light penetrates the superimposed window zones, the number of stacked value documents can be determined by way of the overall rotation of the polarization plane P A , P B . The overall nominal value of a stack of banknotes can thus be determined. The window zones can have category-specific rotational characteristics for different categories or nominal values and/or can be disposed in category-specific positions in the valuable document.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase of International Application Ser.No. PCT/EP2002/014507, filed Dec. 18, 2002.

FIELD OF THE INVENTION

The invention relates to a method for testing of documents of value,such as the determination of authenticity, number and/or category ofbanknotes, as well as documents of value adapted to same and anapparatus for carrying out the method.

DESCRIPTION OF THE BACKGROUND ART

Documents of value within the meaning of the present invention areparticularly understood to mean documents of value with a predeterminednominal value, thus in particular banknotes, but also shares, postagestamps and the like. The invention is also applicable to other documentsof value without a nominal value, such as checks, credit cards, IDcards, etc. and is suited in particular for the classification andquantity determination of such documents of value with no nominal value.In the following, the invention is described by way of example withreference to the particular problems encountered in banknote processing.

SUMMARY OF THE INVENTION

Determination of the authenticity and/or the category and/or the nominalvalue of banknotes is effected inter alias on the basis of different,automatically detectable banknote features, for example, on the basis ofthe printed image, the coloration, the dimensions, the labeling and thelike, which features are usually designed such that they arenominal-value-specific. In this context, e.g. the determination of totalnominal value of a stack of banknotes is elaborate, since, particularlyin the presence of banknote bundles with mixed denominations, thebanknotes must be singled first, in order to be able to determine theirrespective nominal value.

The object of the present invention consists in proposing a new methodfor checking documents of value, which in particular can also be appliedfor simple evaluation of documents of value that are presentindividually or bundled, which can also be of different categories, suchas banknotes of different nominal values. In addition, the object of thepresent invention consists in proposing both suitable documents of valueand an apparatus for carrying out the method.

According to the invention, the documents of value are provided with awindow area that a polarization element is assigned to, which element,by a defined angle, rotates a plane of polarization of light passingthrough the window area. This property is also referred to as rotationalcharacteristic in the following. These window areas can be a componentof one or several see-through windows in the document of value. In thiscontext, an associated see-through window in the document of value canalso comprise one or several such window areas.

The invention offers the particular advantage that, amongst otherthings, the number of a plurality of stacked documents of value can bedetermined exactly by polarized light being radiated through the windowareas lying one on top of the other and the overall rotation of theplane of polarization being measured. Since the rotation of the plane ofpolarization is predetermined for a single document of value, the numberand aggregate value of the stacked documents of value can readily beinferred from the measured total rotation. Moreover, a criterion fordetermining the authenticity of the document of value is hereby alsogiven.

In this context, so-called “optically active” elements, which alsoexhibit a polarization-plane-rotating effect without outside electricalor magnetic fields, are preferentially used as polarization elements.These are e.g. crystal structures out of quartz, iron garnets and/orgallium garnets, sodium chlorate or sodium bromate. A polymer foilpresent in the window area has proven to be especially suitable as anoptically active element. Polymeric, optically active elements, e.g.also in the form of polymer dispersed liquid crystals, are known to theexpert. Such polymer foils can be manufactured inexpensively and withdifferent polarization properties. The polymer foil can be integratedinto the window area or, instead, the window area can be formed of thepolymer foil itself. Techniques for embedding polymer foils in paper aswindows are sufficiently known and readily integratable in manufacturingprocesses.

Alternatively, substances with a polarization-plane rotating effectinduced through external electrical or magnetic fields can also be usedas polarization elements. Application of the Faraday effect proves to beparticularly advantageous in this regard. However, substances withcircular birefringent effect, which either occurs of itself or isinduced by external fields, can also be used. Thus, opticallyanisotropic substances can be used, which are irradiated along theiroptical axis in order to eliminate the natural birefringent effect.

Since the detected position of the plane of polarization basicallyvaries between 0° and 180°, while the total rotation, though, can go farbeyond 180° depending on the rotational characteristic of the windowareas and the number of stacked documents of value, according to apreferred embodiment, the rotational characteristic of the window areasshould be adjusted such that the actually measured rotation of the planeof polarization, which is in the range of 0° to 180°, permits anunequivocal statement about the number of documents of value containedtherein for large stacks of documents of value as well.

If the rotational characteristic of the individual documents of valuecan be measured precisely e.g. to a few powers by the detector formeasuring the rotation of the plane of polarization, and if the rotationangle for a single document of value is selected such that it does nothave a small common multiple with 180°, the exact number and value ofthe banknotes can also be determined when a stack of banknotes withseveral banknotes is being measured.

Alternatively or additionally, a preferred embodiment provides that atleast two window areas with different characteristics are provided. If,in this case, e.g. a separate light beam is radiated through one of therespective window areas one will be able to achieve, through suitableselection of the different rotation properties, that the respectiverotations of the plane of polarization of the individual beams throughthe individual areas that are detected using measurement technology willbe so far apart that it will be possible to reliably derive from samethe number of documents of value even of thick stacks of documents ofvalue.

Moreover, it is especially preferentially conceivable to take account ofthe light absorption during passage of the light through the window areaor, as the case may be, the window areas when determining the number ofthe documents of value of the document-of-value stack. This is becausethe greater the number of the stacked documents of value is, the morelight is absorbed, and comparison with a reference table then gives anindication of the number of the stacked documents of value.

An embodiment of the invention provides that documents of value, whichbelong to different categories of documents of value, possess differentcategory-specific window areas, so that, from a group of documents ofvalue, each document of value is identifiable according to its category.

In the case of documents of value with different nominal values, suchas, for example, in the case of banknotes, the nominal value of theindividual document of value and, in a single measuring process inparticular, the aggregate value of a bundle of banknotes which alsocontains mixed nominal values can be determined in this manner. In thecase of a check, for example, a distinction can be made betweendifferent check forms.

According to a preferred embodiment, the category-specific window areasdiffer from one another in that they are present relative to a referencecorner or a reference edge at a category-specific position of thedocuments of value.

It is thereby ensured in an especially simple fashion, that it isimmediately recognizable, whether there are documents of value ofdifferent categories in a stack of documents of value. This is because,under these conditions, a document of value of a certaindocument-of-value category would block the passage of light through thewindow area of a document of value of different document-of-valuecategory within the same document-of-value stack. Such a document ofvalue that has erroneously found its way into the document-of-valuestack can then be removed and determination of the number of the stackeddocuments of value be performed. This approach is thus also particularlysuitable for automatic counting and determination of value of bundles ofdocuments of value.

Alternatively or additionally, the category-specific window areaspreferentially differ from one another in that they possess acategory-specific rotational characteristic by rotating a plane ofpolarization of light, which passes through, by a category-specificangle.

This can e.g. be achieved by selecting different materials for thedifferent documents of value.

Dependent on the measured rotation, the category of the document ofvalue can then be determined. The number and aggregate value of stackeddocuments of value, which either belong to the same or differentcategories, can also be determined in the above-described fashion on thebasis of the total rotation. The rotational characteristics of theindividual document-of-value categories should be matched such that therotation, which is detected using measurement technology, can beassigned unequivocally to a certain number of stacked documents of valueof the individual document-of-value categories. In this way, the totalnominal value of a bundle of documents of value can thus e.g. also bedetermined with a single measuring process.

The variants mentioned above are again preferentially used for alsomeasuring documents of value of one category. Accordingly, e.g. therotation angles can be selected for the individual documents of value ofdifferent categories, like e.g. banknotes of different nominal values,such that they have no small common multiple in comparison to oneanother and/or in comparison to 180°, so that their number and value canalso be determined exactly when measuring a stack with several documentsof value. Alternatively or additionally, use of documents of value withat least two window areas or, as the case may be, consideration of theattenuation of the intensity of the light radiated through the windowareas of the stack of documents of value is again possible as well.

If documents of value of different categories are present, in this case,the window areas can be present at the same position of the documents ofvalue relative to a reference corner or reference edge. By e.g. a stackof such documents of value being aligned flush to this corner or edge,it becomes possible to achieve overlapping of the window areas of theindividual documents of value of the stack in a simple fashion.

An especially preferred embodiment, with which the documents of value ofa stack of documents of value can be determined both according to thecategory and according to the number within the same category, providesthat documents of value of a group of documents of value possess one ormore window areas at a category-specific position in the document ofvalue and additionally possess further window areas, which, however, donot influence the plane of polarization of the light passing through, atsuch positions in the document of value, where the documents of value ofother categories in turn possess window areas with category-specificpositions.

It is thereby achieved that the light at all positions, where at leastone document of value possesses a window area with a category-specificposition, can penetrate the entire stack of documents of value, and thetotal rotation of the plane of polarization at each category-specificposition is only influenced by documents of value of the same category.In this manner, an unequivocal statement about the number of documentsof value of a certain category within a document of value stack can beobtained by means of the respective window area position and therotation of the plane of polarization detected at this position by theuse of measurement technology.

The document of value preferentially possesses at least four identicalwindow areas with an optically active element at positions, for whichthe central longitudinal axis and the central transverse axis of thedocuments of value, which are usually rectangular, represent axialsymmetry axes. It is thereby ensured that, independently of itsposition—be it lying on the front side or back side, be it upside downor not,—the document of value comes to rest with one of the fouridentical window areas over a correspondingly disposed detector fordetermining the position of the plane of polarization of the polarizedlight passing through the document of value.

The individual documents of value or the stack of documents of value canbe transported over the detector continuously or intermittently. Then,it is expedient for the window areas in all of the documents of value tobe disposed along a line in accordance with the direction of transportof the documents of value, independently of their number andindependently of the document-of-value category, so as to be detected bythe detector. The use of a single detector then already suffices tocheck all of the window area positions.

According to a further preferred embodiment, the banknotes areadditionally provided with a polarizing filter. This filter can be usedto check the polarization rotation of the polarization-rotating windowareas. For this purpose, e.g. two banknotes are placed on top of anothersuch that the polarization-rotating area of the one banknote issuperimposed over the polarizing filter of the other banknote. Dependingon the rotational position of the two areas with reference to oneanother, light passing through is blocked. In this manner, with regardto a check of the authenticity of the banknotes, it is simple toascertain whether the window areas of the banknotes are a forgery in theform of a transparent foil without any optically active effectwhatsoever. Since the polarization-rotating area of the banknote and thepolarizing filter occupy different areas of the banknote surface, thetwo banknotes will preferentially have to be disposed such that they areoffset in their outside contour to one another. However, this does notrepresent a problem for an authenticity check by hand.

As an alternative to the aforementioned, the authenticity of a singledocument of value can already be checked by the banknote to be checkedbeing bent such that a polarization-rotating area and the polarizingfilter of the same banknote overlap.

According to a further separate idea, e.g. the polarization-rotatingwindow areas are designed as transmission filters, in particular as edgetransmission filters, in the case of which the filter absorbs or, as thecase may be, transmits is significantly more strongly above a limitwavelength than below the limit wavelength. A filter can also exhibitseveral such edges. If, in the case of documents of value of differentcategories, e.g. banknotes of different nominal values, the limitwavelengths are different, this can be utilized in a simple manner tocheck whether a banknote with a wrong nominal value is contained in abundle of banknotes. Although, the limit wavelengths can also be in thevisible spectral range, they will preferentially be in the infraredrange. In this context, the window areas of the stacked banknotes, whichwindow areas are disposed one on top of the other, are irradiated withlight of a wavelength, which e.g. is only permeable for the transmissionfilter area of the banknote nominal value that is about to be tested. Ifthe light is blocked during transmission, one can then consequentlyconclude that at least one banknote of another nominal value is presentin the stack.

However, checking of the documents of value or stacks of documents ofvalue can also be stationary. Then, the position of the particularwindow areas is not critical. However, several light sources forirradiating the individual window areas and, in particular, severaldetectors for detecting the position of the plane of polarization of thelight passing through the window areas may perhaps be needed then.

In particular, in the case of such a stationary check, the apparatus canpossess a positioning device in order to bring the documents of value,individually or stacked, into a defined, aligned position, in which thelight is radiated vertically through the window areas of the documentsof value. This positioning device will e.g. be designed such that thedocuments of value are inputted or, as the case may be, fed inclined ande.g. are aligned against a stop on account of their gravity.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments and advantages of the invention are explained withreference to the figures.

They show:

FIG. 1 a top view of a banknote with a window area according to theinvention;

FIG. 2 a view in perspective of the banknote from FIG. 1 with thepolarized light passing through the window area;

FIG. 3 a banknote according to FIG. 1, but with several window areaswith different rotational characteristics;

FIG. 4 a view in perspective of several stacked banknotes according toFIG. 3 with differently rotated, polarized light beams passing throughthe window areas;

FIG. 5 a diagram-like depiction of the dependence of the rotation of theplane of polarization on the rotational characteristic and number ofwindow areas through which the light passes;

FIG. 6 a banknote according to FIG. 3, but with four identical, axiallysymmetrically disposed window areas;

FIG. 7 a banknote with a different nominal value and window areaspositioned differently from the banknote according to FIG. 6;

FIG. 8 a banknote with nominal-value-specific andnon-nominal-value-specific window areas; and

FIG. 9 an apparatus for determining the total nominal value of a stackof banknotes.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a document of value 1, in particular a banknote, with awindow area 2 with an optically active element as a polarizationelement. The optically active element is formed by a polymer foil thatspans the entire see-through window 2. In this embodiment,polarization-plane rotating window area 2 thus corresponds to the totalsurface of see-through window 2, although it could alternatively also bepresent only in a partial area of the entire see-through window 2.Window area 2 is formed quadratically in the embodiment, but it canpossess any desired form, in particular, also a round form. The windowarea, i.e. the optically active element forming the window area, causesa rotation of the plane of polarization of light passing through windowarea 2. This is shown in perspective in FIG. 2, where a linearlypolarized light beam L, the polarizing angle of which is designated byan arrow marked with P₀, passes through window area 2, with the angularposition of the plane of polarization of the light beam changing uponpassage through window area 2 and then being marked with P_(A). Therotation of the plane of polarization results at P₀ minus P_(A) and isidentical for all banknotes with the same nominal value. For example,the window areas can be adjusted such that the plane of polarization ofbanknotes with a nominal value of DM 10 is rotated by 3° and that ofbanknotes with a nominal value of DM 100 by 10°. This way, individualbanknotes can be differentiated according to nominal value, withmeasurement of the rotation of polarization being able to beadditionally used as a criterion of authenticity. In this case, however,it is not possible to differentiate between 10 stacked DM 10 banknotesand 3 stacked DM 100 banknotes, as the total rotation amounts to 30° ineach case.

FIG. 3 shows a further development of the banknote from FIG. 1, whichpossesses two window areas 2A, 2B with different properties. The planeof polarization of light, which passes through window area 2A, isrotated by a defined angle that is different from the plane ofpolarization of the light passing through window area 2B.

In FIG. 4, this is depicted with reference to a stack of banknotes 10with four banknotes 1 of the same denomination. This means that each ofbanknotes 1 possesses identical window areas 2A, 2B at identical places.The position of the plane of polarization of the two light beams L_(A)or, as the case may be, L_(B) passing through window areas 2A, 2B isidentical prior to entry into the first banknote and marked with P₀ inFIG. 4. Upon exit from the last banknote, the plane of polarization oflight beam L_(A) that has passed through window areas 2A has rotated byan angle P_(A) minus P₀, and the plane of polarization of light beamL_(B) that has passed through window areas 2B has rotated by an angleP_(B) minus P₀ differing from said angle.

This is expedient in order to reliably determine the amount of a largernumber of stacked banknotes. The problems underlying the foregoing areexplained with reference to FIG. 5 in the following. FIG. 5 shows therespective rotations P of the plane of polarization marked as P_(A) or,as the case may be, P_(B) for a stack of banknotes with window areas 2Aand 2B in dependence on the number of banknotes n of the stack ofbanknotes. Accordingly, 14 window areas 2A stacked one on top of theother cause a rotation of the plane of polarization by precisely 180°,so that the number of banknotes in a stack of banknotes can only bedetermined precisely if the stack of banknotes contains 13 or fewerbanknotes. The same applies to banknotes with window areas 2B, of which18 banknotes stacked one on top of the other cause a rotation of theplane of polarization by 180°. Here, the maximum number of banknotesstacked on top of one another that can be determined unequivocally is17. By now combining window areas 2A, 2B in a banknote and by the factthat, in their combination, they are specific for a certain banknotenominal value, this problem can be overcome, as the case where therotation of the plane of polarization simultaneously amounts to 180° or,as the case may be, a multiple of 180° for both window areas only occursfor stacks of banknotes with an unrealistically large number ofbanknotes. For a stack of banknotes with a realistic number ofbanknotes, the combination of window areas 2A, 2B permits an unequivocalconclusion regarding the number and, in the case of banknotes withdenomination-specific rotation characteristics, regarding the categoryof the stacked banknotes as well, so that the total denomination of thestack of banknotes can be determined.

FIG. 6 shows a further advantageous embodiment of the invention,according to which are provided four identical window areas 2A, 2B in abanknote 1, and according to which there is a window area 2A and awindow area 2B in each corner of the banknote. The position of thewindow areas is selected such that longitudinal central axis 18 andtransverse central axis 19 of banknote 1 represent axial symmetry axesfor window areas 2A, 2B. Such a banknote can be aligned laterallyreversed or upside down relative to reference point O, as shown in FIG.6, and a window area 2A and a window area 2B always lies on a concretepoint relative to reference point O. This has the advantage thatdetectors must only be provided at this concrete point to determine theposition of the plane of polarization and that true-to-side positioningof the banknotes does not need to be considered during the check.

Whereas window 2 or, as the case may be, 2A, 2B can perfectly well bepresent at the same position within the banknotes for banknotes ofdifferent denominations and only differ as to their rotationcharacteristics, an alternative embodiment, depicted in FIG. 7, providesthat the one window area or, as the case may be, window areas 3, 3A, 3Bof a banknote, the denomination of which differs from that of thebanknote depicted in FIGS. 1, 3 and 6, is present at a differentposition than window areas 2 or, as the case may be, 2A, 2B. Thedenomination or, as the case may be, the nominal value of banknotes canthen be determined solely on the basis of the position of respectivewindow areas 2 and 3 within the banknote. Preferentially, window areas2, 3 can also exhibit a nominal-value-specific rotational characteristicin addition to their nominal-value-specific position. Beyond that, inbanknote 1 depicted in FIG. 7 as well, window area 3 can be subdividedinto window areas 3A, 3B with different rotational characteristicsand/or be present in identical quadruplicate in the banknote, asindicated in FIG. 7 by chain lines in each case.

A special additional embodiment of the invention is depicted in FIG. 8and shows a banknote 1 with several window areas in 2′, 3′, 4, 5′, 6′,7′, 8′. Only window area 4 exhibits a rotational characteristic and inthe embodiment is formed by two window areas 4A, 4B with differentrotational characteristics. The remaining window areas 2′, 3′ and 5′ to8′ marked with ′ are designed as a transparent foil without rotationalcharacteristics. In other words, the plane of polarization of light thatpasses through these window areas is not influenced by the window areaswithout rotational characteristics. In the case of banknote 1 depictedin FIG. 8 as well, the window areas are again provided symmetrically inquadruplicate in order to permit orientation-independent checking of thebanknote. Whereas the denomination of the banknote depicted in FIG. 8can be determined on the basis of the rotational characteristic ofwindow area 4, a correspondingly constructed banknote with a differentnominal value could be determined on the basis of the rotationalcharacteristic of another window area, and in this case, window area 4would be designed as a transparent foil and marked with 4′. If one nowstacks several banknotes, the window areas of which are disposed inaccordance with the representation according to FIG. 8, but whichpossess different nominal values and, as a result, different windowareas with rotation-angle characteristic properties, it will be possibleto determine the banknote number present in the stack of banknotes forevery banknote nominal value by checking every single window areaposition and use this result to determine the total nominal value of thestack of banknotes.

FIG. 9 shows an apparatus for stationary checking of a single banknote 1or several stacked banknotes that can be employed in a banknoteprocessing apparatus. The embodiment depicted in FIG. 9 is adapted, byway of example, to checking banknotes or, as the case may be, stackedbanknotes according to FIGS. 3 and 4, the window area 2 of which issubdivided into two window areas 2A, 2B with different rotationalcharacteristics. Beyond that, the window areas of the banknotes to bechecked are positioned identically within the banknotes independently oftheir denomination, in order to ensure that the light beams passingthrough the stack of banknotes 10 are detected by detectors 16A, 16B.Light beams L are generated in a light source 11 and are polarizedlinearly by means of a polarizing filter 12. Alternatively, a laser canalso be used as a light source for generating linearly polarized light.Stack of banknotes 10 lies on a receiving plane 13 serving as a devicefor receiving documents of value, and the edges of the individualbanknotes of the stack of banknotes 10 run into stop faces 14 and 15,which are disposed at right angles to one another. As a result, thecorrect alignment of the banknotes with their window areas relative tolight source 11 and detectors 16A, 16B is ensured so that light beams Lhit detectors 16A, 16B vertically through the window areas. Alignment ofthe stack of banknotes 10 is preferentially effected independentlythrough an inclined arrangement of the total apparatus as indicated bythe gravity arrow g so that the banknotes independently lie flat againststop surfaces 14, 15 on account of the effect of gravity.

An evaluation device 17 is connected to detectors 16A, 16B via signallines 20. From the angular positions of the planes of polarization oflight beams L and the original position of the plane of polarization oflight beams L, which is predetermined by polarizing filter 12,evaluation device 17 determines the angular amount, by which the planeof polarization has rotated due to the passage through the window areas.As explained previously, this is then used to determine the authenticityand/or nominal value and/or the number and/or the total nominal value ofthe banknote situated in the apparatus.

Detectors 16A, 16B can additionally be designed to measure the lightintensity of the light detected, in order to be able to infer the numberof banknotes situated on deposit plane 13. The evaluation of the lightintensity value, in turn, is effected in evaluation device 17. Ofcourse, additional detectors can also be provided for this purpose.

In this context, the embodiment depicted in FIG. 9 can be formed as astationary variant where the banknotes are deposited on the depositplane individually or as a bundle, e.g. also manually, and then measuredas described hereinabove. Particularly in such a case as well, theapparatus can e.g. be a manual device or a tabletop device, which, forexample, is used in banks, department stores or other places wherelarger quantities of banknotes accrue, in order to simply, quickly andreliably determine by means of a single measuring process the number ofbanknotes of each nominal value and, in particular, also the totalnumber and aggregate value of banknotes of a banknote bundle.

Alternatively, this apparatus can also be designed with slightmodifications as part of a banknote processing machine, such as of asorter or an automatic teller, where e.g. the banknotes' authenticityand/or fitness for circulation are checked additionally on the basis offurther banknote features. In this case in particular, the banknotes canalso be transported individually or bundled through the measuring areabetween the light source and the detector by means of a transportapparatus.

As an additional embodiment of the aforementioned checking apparatus,this can e.g. comprise a non-depicted magnetic field generator that cangenerate a magnetic field, which runs parallel to the direction ofpropagation of light beam L in the area of receiving plane 13. Indocuments that basically do not exhibit a polarization-plane rotatingeffect, such an effect can hereby also be produced by means of theFaraday effect.

1. Document of value comprising: at least one window area; and apolarization element disposed in the at least one window area; wherein,the polarization element rotates a plane of polarization of a linearlypolarized light beam passing through the at least one window area, by apre-defined angle, and wherein the angle is defined so that a plane ofpolarization of a linearly polarized light beam passing through windowareas of several of said documents of value lying on top of the other isrotated by a corresponding multiple of the angle, and the polarizationelement is an element, which, induced by at least one of an outsideelectrical and magnetic field, rotates the plane of polarization of thepolarized light beam passing through the associated window area by thedefined angle.
 2. Document of value according to claim 1, characterizedin that the polarization element is an optically active element, which,even in the absence of at least one of an outside electrical andmagnetic field rotates the plane of polarization of the polarized lightbeam passing through the associated window area by the defined angle. 3.Document of value according to claim 1, characterized in that thepolarization element is an element, which, in the presence of a magneticfield that is parallel to the light beam, rotates the plane ofpolarization of the polarized light beam passing through the associatedwindow area by the defined angle.
 4. Document of value according toclaim 1, characterized in that the polarization element is an opticallyanisotropic substance with an optical axis which runs perpendicularly toa surface of the window area.
 5. Document of value according to claim 1,characterized in that the polarization element comprises a polymer foilpresent in the window area.
 6. Document of value according to claim 1,characterized by several window areas, which rotate by different definedangles the plane of polarization of the polarized light beam passingthrough the associated window area.
 7. Document of value according toclaim 1, characterized in that the document of value possesses a centrallongitudinal axis and a central transverse axis and that four windowareas are provided, for which the central longitudinal axis and thecentral transverse axis of the document of value form axial symmetryaxes.
 8. Document of value according to claim 1, characterized in thatat least one of the window areas of the document of value possess aproperty that is specific for the category of the document of value. 9.Document of value according to claim 8, characterized in that thespecific property includes that corresponding window areas rotate theplane of polarization of polarized light passing through by acategory-specific angle.
 10. Document of value according to claim 8,characterized in that the specific property includes that the elementsof corresponding window areas are composed of a different material. 11.Document of value according to claim 8, characterized in that thespecific property includes that corresponding window areas are presentrelative to a reference corner or reference edge of the document ofvalue at a category-specific position of the document of value. 12.Document of value according to claim 11, characterized in that, inaddition to a corresponding window area having a category-specificposition, the document of value possesses one or more window areas,which do not rotate the plane of polarization of polarized light passingthrough, at such positions of the document of value, where documents ofvalue of other categories in turn possess window areas with acategory-specific position.
 13. Document of value according to claim 8,characterized in that, in a case of documents of value of differentcategories, the window areas are present relative to a reference corneror reference edge of the document of value at the same position of thedocument of value.
 14. Document of value according to claim 1,characterized in that the document of value exhibits a window area thatacts as at least one of a polarizing filter and a transmission filter.15. Method for checking at least one document of value characterized inthat it has a polarizing window area, the method comprising: radiating abeam of linearly polarized light through the window area of the documentof value; measuring an angle of rotation of the plane of polarization ofthe light beam passing through the window area; performing a check independence on the measured angle of rotation of the plane ofpolarization; and wherein documents of value of a bundle of documents ofvalue are stacked one on top of another such that window areas ofindividual documents of value lie one on top of another, the polarizedlight beam is radiated through window areas, which are disposed onebehind another, of the documents of value, and at least one of a number,and category, and the total nominal value of all documents of value ofsaid bundle is determined in dependence on the rotation of the plane ofpolarization.
 16. Method according to claim 15, characterized in that,when the rotation of the plane of polarization is measured, at least oneof an electrical and magnetic field is generated at least in an area ofthe document of value such that the polarization-plane rotation isinduced in a polarization element that is present in a window area. 17.Method according to claim 16, characterized in that, when the rotationof the plane of polarization is measured, at least one of a magneticfield that is parallel to polarized light beam is generated at least inan area of the document of value.
 18. Method according to claim 15 fordetermining at least one of a number and category of at least onedocument of value, characterized in that the document of value comprisesa plurality of window areas with one element each, which rotate theplane of polarization of polarized light passing through an associatedwindow area by different angles, with the polarized light beam beingradiated through the plurality of window areas, the rotations of theplane of polarization of the light beam passing through the plurality ofwindow areas being measured separately for each window and the number,category, a total nominal value of the documents of value or acombination thereof being determined in dependence on the measuredrotations of the plane of polarization.
 19. Method according to claim 18for determining the number and category of stacked documents of valuewith different category affiliations, characterized in that all or atleast part of the documents of value possess, additionally to a windowarea at a category-specific position, further window areas, which do notrotate the plane of polarization of polarized light passing through, atsuch positions of the document of value, where the documents of valuewith a different category affiliation in turn possess window areas witha category-specific position, with the polarized light beam beingradiated through the window areas at different category-specificwindow-area positions, the rotations of the plane of polarization of thepolarized light beam passing through the window areas being measuredseparately for each category-specific window-area position and thenumber and category of the stacked documents of value being determinedin dependence on rotations of the plane of polarization measured foreach category-specific window-area position.
 20. Method according toclaim 15, characterized in that light absorption when the light beampasses through said window area or is taken into account when a numberof stacked documents of value is determined.
 21. Apparatus for checkingat least one of a number and category of stacked or individual documentsof value comprising: a document-of-value receiving device for receivingdocuments of value; a checking device with at least one light source forradiating polarized light onto the document-of-value receiving device onone side of the document-of-value receiving device and with at least onedetector for detecting, on another side of the document-of-valuereceiving device, polarized light sent out by the light source ontodocument-of-value receiving device, with the at least one detector beingdesigned to detect the orientation of a plane of polarization ofpolarized light; an evaluation device connected to the checking devicevia a signal line, which performs a check of one or more documents ofvalue situated in the checking device in dependence on a rotation of theplane of polarization of the polarized light obtained on the basis ofthe orientation of the plane of polarization detected by the checkingdevice; and wherein the document-of-value receiving device comprises apositioning device in order to bring documents of value into a defined,aligned position stacked.
 22. Apparatus according to claim 21,characterized in that the checking device further comprises a fieldgeneration device in order to generate at least one of an electrical andmagnetic field at least in an area of the document-of-value receivingdevice.
 23. Apparatus according to claim 22, characterized in that thefield generation device comprises a magnetic-field generation device,which generates, at least in the area of the document-of-value receivingdevice, a magnetic field which is parallel to the light radiated by thelight source.
 24. Apparatus according to claim 21, characterized in thatthe checking device comprises one or more light sources in order to,with a document of value with several window areas radiate light throughdifferent window areas, with the evaluation device performing adetermination of at least one of a number and category of the documentof value situated in the checking device in dependence on the rotationsof the plane of polarization of the polarized light detected separatelyfor each of the plurality of window areas by means of the checkingdevice.
 25. Apparatus according to claim 21, characterized in that thechecking device is designed to detect the extent to which light isabsorbed by the documents of value situated in document-of-valuereceiving device, and that the evaluation device performs thedetermination of a number of the documents of value in dependence on thedetected light absorption.
 26. Apparatus according to claim 21,characterized in that positioning device is disposed inclined relativeto a horizontal position.
 27. Apparatus for processing documents ofvalue with an apparatus according to claim
 21. 28. The document of valueof claim 1, comprising a banknote.
 29. The document of value of claim14, wherein said filter is an edge transmission filter.
 30. The methodof claim 15 where said document of value is a banknote.
 31. The methodof claim 15 wherein said check is at least one of a determination ofauthenticity, a determination of number or a determination of a categoryof said document of value.
 32. The apparatus of claim 21 wherein saiddocuments of value are banknotes.
 33. The method of claim 21 whereinsaid check is a determination of authenticity, a determination of numberor a determination of a category of said documents of value.
 34. Theapparatus of claim 27 wherein said documents of value are banknotes.